The present invention relates to a method for preparing food products by means of processing food particles with a gelling agent, a device suitable for performing the above described method, a food product obtainable with the method of the present invention and the use of an acidic buffer solution for stabilizing food products.
The general principle of producing foods by means of extrusion is already known in the prior art. It has become possible by means of extrusion to manufacture foods with a specific composition and shape at a relatively high production speed. Extrusion is particularly a commonly used method in the production of sausage.
A particular form of extrusion is so-called co-extrusion. The principle of co-extrusion in food products is described in, among others, Netherlands patent NL 6909339. This document describes the coating of a strand of food dough with a coating layer of collagen by means of co-extrusion. Following extrusion the coated strand is guided for strengthening purposes through a coagulation bath. Under the influence of the coagulation solution the collagen coagulates and/or precipitates and the coating layer is strengthened. A strand of food dough is thus formed which is at least partially coated with a strong coating layer of collagen, i.e. casing.
Extruded food may also be used in moulding machines for moulding three-dimensional products from a meat mass or the like. International patent application WO 00/30458 A1 describes various methods and moulding machines for moulding products. For example, U.S. Pat. No. 4,987,643 describes a moulding machine of the ‘slide-plate’ type, for the purpose of producing portions of hamburger meat. Another known type of moulding machine for meat products and the like is the ‘turrent-type’, see for example U.S. Pat. No. 4,193,167. Additionally, extruded food may also be used in ‘rotating drum type’ moulding machines. See for examples of ‘rotating drum type’ moulding machines U.S. Pat. No. 3,504,639, U.S. Pat. No. 3,851,355, U.S. Pat. No. 4,212,609, GB 2,259,043, FR 2,491,734 and FR 2,538223. In case of using moulding methods for producing food products, the extruded food fed to the mould cavities of the moulding machine must have a suitable viscosity to reduce the filling pressure needed to fill the mould cavities with a sufficient amount of extruded food. In order to change the viscosity of the extruded food during the moulding process, collagen might be used.
In addition to proteins such as collagen, use is often also made in the food industry of polysaccharides, such as alginate, as coating agent for foods such as for instance sausage. The term “alginate” refers to a group of naturally occurring polysaccharides extracted from seaweed. In the presence of alkaline earth metals (such as, among others, magnesium and calcium) alginates can form gels relatively easily. Collagen and alginate may also be used in combination as it is described in International patent application WO 2006/135238 A2.
Studies have shown that the gelling of alginates under the influence of for instance calcium results due to the development of a three-dimensional structure. This is also referred to as the so-called egg-box model. When alginate is transformed into this three-dimensional structure, a relatively strong gel is created. Such a gel is highly suited to serve as coating layer of, for instance, a sausage or in providing extruded food products suitable for moulding machines.
In the co-extrusion practice a coating layer of alginate is often extruded onto a food dough strand in the making of sausage. The coating layer of the at least partly coated strand is then strengthened. Guiding the extruded and coated strand through a salt bath containing calcium provides the strengthening. Due to the presence of the calcium the coating agent, e.g. the alginate, will gel quickly and a strong gel coating layer forms on the food dough strand.
In the moulding practice alginate or collagen is used to provide extruded food having a preferred viscosity. The extruded food may be strengthened subsequently by providing calcium to the food product.
A drawback however is that the initial strength of the alginate gel is weakened over time, e.g. 24 hours, due to metal chelating agents (e.g. phosphates) present in the food dough dissolving the divalent ion, e.g. calcium, which is bound to the gelling agent. The removal of divalent ions from the gel causes the gelling agent to swell and to disrupt. In worst cases the gel disappears completely and consequently the co-extruded food or moulded food is no longer stable and falls apart.
An additional drawback of the alginate gel known in the art is that the gel as such does not adhere to the food dough. As a consequence the cooking characteristics of a co-extruded food product, e.g. sausage, are such that during cooking the gel coating does not shrink together with the food dough and that the cooking heat is not distributed through the food. This results in a heat build-up in the gel coating which causes unwanted deformation and discoloration of the coating due to evaporation of the moisture in the coating. Furthermore, air bubbles may form between the food dough and the casing during cooking, which results in a less attractive product and/or insufficient cooking at least locally.
The cooking characteristics of a moulded food product, e.g. hamburger, may be such that the product easily falls apart.
In view of the above there is a need to stabilize and increase the strength of moulded food products and/or co-extruded food products wherein alginate gel is applied to the co-extruded food dough to enhance storage duration. Increasing the amount of divalent ions, e.g. calcium, strontium, barium or combinations thereof, has been provided in the prior art. However, an increased amount of divalent ions result in variations in taste, e.g. bitter taste, possibly a relatively high salt consumption and corrosion of the equipment.
Furthermore, there is a need of increasing the adherence between the gelling agent and the food dough together in order to increase the cooking characteristics of the food product. The present invention provides a solution for both drawbacks.